In a mobile communication system, a user equipment is able to receive information from a base station in downlink and the user equipment is able to transmit information in uplink as well. The information transmitted/received by the user equipment includes a data and various control informations. Various physical channels may exist according to a kind and usage of the information transceived by the user equipment.
FIG. 1 is a diagram for explaining physical channels used for 3GPP (3rd generation partnership project) LTE (long term evolution) system and a method of a signal transmission using the same.
If a power of a user equipment is turned on or the user equipment enters a new cell, the user equipment may perform an initial cell search job for matching synchronization with a base station and the like [S101]. To this end, the user equipment may receive a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH) from the base station, may match synchronization with the base station and may then obtain information such as a cell ID and the like. Subsequently, the user equipment may receive a physical broadcast channel from the base station and may be then able to obtain intra-cell broadcast information. Meanwhile, the user equipment may receive a downlink reference signal (DL RS) and may be then able to check a DL channel state.
Having completed the initial cell search, the user equipment may receive a physical downlink control channel (PDCCH) and a physical downlink shared control channel (PDSCH) according to the physical downlink control channel (PDCCH) and may be then able to obtain a detailed system information [S102].
Meanwhile, the user equipment, which does not complete an access to a base station, may be able to perform a random access procedure to complete the access to the base station [S103 to S106]. To this end, the user equipment may transmit a specific sequence as a preamble via a physical random access channel (PRACH) [S103] and may be then able to receive a response message via PDCCH and a corresponding PDSCH in response to the random access [S104]. In case of a contention based random access except a handover case, it may be able to perform a contention resolution procedure such as a transmission [S105] of an additional physical random access channel and a channel reception [S106] of a physical downlink control channel and a corresponding physical downlink shared channel.
Having performed the above mentioned procedures, the user equipment may be able to perform a PDCCH/PDSCH reception [S107] and a PUSCH/PUCCH (physical uplink shared channel/physical uplink control channel) transmission [S108] as a general uplink/downlink signal transmission procedure.
FIG. 2 is a diagram for describing a signal processing process for a user equipment to transmit a UL signal.
First of all, in order to transmit a UL signal, a scrambling module 210 of a user equipment may be able to scramble a transmission signal using a UE-specific scrambling signal. This scrambled signal is inputted to a modulating mapper 220 and is then modulated into a complex symbol by BPSK (binary phase shift keying), QPSK (quadrature phase shift keying) or 16 QAM (quadrature amplitude modulation) in accordance with a type and/or channel state of the transmission signal. Subsequently, the complex symbol is processed by a transform precoder 230 and is then inputted to a resource element mapper 240. In this case, the resource element mapper 240 may be able to map the complex symbol to a time-frequency resource element, which shall be used for practical transmission. This processed signal is inputted to an SC-FDMA signal generator 250 and may be then transmitted to a base station via antenna.
FIG. 3 is a diagram for describing a signal processing process for a base station to transmit a DL signal.
In 3GPP LTE system, a base station may be able to transmit at least one codeword in DL. Hence, each of the at least one codeword can be processed into a complex symbol by a scrambling module 301 and a modulating mapper 302. The complex symbol may be then mapped to a plurality of layers by a layer mapper 303. Each of a plurality of the layers may be then assigned to each transmitting antenna by being multiplied by a prescribed precoding matrix selected by a precoding module 304 in accordance with a channel state. A per-antenna transmission signal processed in the above manner is mapped to a time-frequency resource element by each resource element mapper 305, enters an OFDM (orthogonal frequency division multiple access) signal generator 306, and may be then transmitted via a corresponding antenna.
In case that a user equipment transmits a signal in UL, PAPR (peak-to-average power ratio) may cause a more considerable problem than a case that a base station transmits a signal in DL in a mobile communication system. Thus, as mentioned earlier in relation to FIG. 2 and FIG. 3, unlike OFDMA scheme used for transmitting a DL signal, SC-FDMA (single carrier-frequency division multiple access) scheme is used for transmitting a UL signal.
FIG. 4 is a diagram for describing a SC-FDMA scheme for a UL signal transmission and OFDMA scheme for a DL signal transmission in a mobile communication system.
Referring to FIG. 4, a user equipment for a UL signal transmission and a base station for a DL signal transmission are identical to each other in including a serial-to-parallel converter 401, a subcarrier mapper 403, an M-point IDFT module 404 and a CP (cyclic prefix) adding module 406.
Yet, a user equipment transmitting a signal by SC-FDMA scheme may additionally include a parallel-to-serial converter 405 and an N-point DFT module 402. In particular, the N-point DFT module 402 enables a transmission signal to have a single carrier property by canceling out an IDFT processing effect of the M-point IDFT module 404. FIG. 5 is a diagram for describing a signal mapping scheme in frequency domain to meet a single carrier property in the frequency domain. FIG. 5(a) indicates a localized mapping scheme and FIG. 5(b) indicates a distributed mapping scheme. The localized mapping scheme is currently defined by 3GPP LTE system.
Meanwhile, a clustered SC-FDMA, which is a modified form of SC-FDMA, is described. According to the clustered SC-FDMA, DFT process output samples in a subcarrier mapping process are divided into subgroups and the subgroups are discontinuously mapped to subcarrier regions, respectively. Occasionally, the clustered SC-FDMA may include a filtering process and a cyclic extension process.
In this case, the subgroup may be named a cluster. And, the cyclic extension may mean that a guard interval longer than a maximum delay spread of a channel is inserted between contiguous symbols to prevent mutual inter-symbol interference (ISI) while each subcarrier symbol is carried on a multi-path channel.